1. Field of the Invention
This invention relates to a method of fabricating a light emitting device, a compound semiconductor wafer, and a light emitting device.
2. Description of the Related Art    [Patent Document 1] U.S. Pat. No. 5,008,718    [Patent Document 2] Japanese Laid-Open Patent Publication No. 2004-128452
A light emitting device having a light emitting layer section thereof composed of an (AlxGa1-x)yIn1-yP alloy (where, 0≦x≦1, 0<y≦1; simply referred to as AlGaInP alloy, or more simply as AlGaInP, hereinafter) can be realized as a high-luminance device, by adopting a double heterostructure in which a thin AlGaInP active layer is sandwiched between an n-type AlGaInP cladding layer and a p-type AlGaInP cladding layer, both having a larger band gap than the active layer.
Taking an AlGaInP light emitting device as an example, by adopting hetero-formation on an n-type GaAs substrate, an n-type GaAs buffer layer, an n-type AlGaInP cladding layer, an AlGaInP active layer, a p-type AlGaInP cladding layer are stacked in this order, so as to form a light emitting layer section having a double heterostructure. Current is applied to the light emitting layer section via a metal electrode formed on a surface of the device. Here, the metal electrode acts as a light interceptor, so that it is formed, for example, so as to cover only a center portion of a main surface of the light emitting layer section, to thereby extract light from the peripheral region having no electrode formed thereon.
In this case, a smaller area of the metal electrode is advantageous in terms of improving the light extraction efficiency, because it can ensure a larger area for the light extraction region formed around the electrode. Conventional efforts have been made on increasing the amount of light extraction by effectively spreading current within the device through consideration on geometry of the electrode, but increase in the electrode area is inevitable anyhow in this case, having been fallen in a dilemma that a smaller light extraction area results in a limited amount of light extraction. Another problem resides in that the current is less likely to spread in the in-plane direction, because dopant carrier concentration, and consequently conductivity of the cladding layer is suppressed to a slightly lower level in order to optimize light emitting recombination of carriers in the active layer. This results in concentration of the current density into the region covered by the electrode, and consequently lowers a substantial amount of the light extraction from the light extraction region.
Thus, there is a publicly-known method of minimizing current density by providing a thick conductive transparent window layer (current spreading layer) between a light emitting layer section and an electrode (Patent Document 1). Also, in order to form a current spreading layer efficiently, there is a publicly-known method of forming a thin light emitting layer section by Metal Organic Vapor Phase Epitaxy Method (Hereinafter also called MOVPE method), on the other hand forming a thick current spreading layer by Hydride Vapor Phase Epitaxial Growth Method(Hereinafter also called HVPE method) (Patent Document 2).